Voltage regulator



Patented Feb. 17, 1931 pm'ran STATES PATENTg QiOI-FICE ABLE m swnmm, Assmxon 'ro ALI-x1111 mm mm:- uuusxa Ax'rmnomenr, or vasrnnas, swnmm, a swnman oonromnon energized by a current proportional to the VOLTAGE mum'ron Application fled Kay 8, 1929, Serial Io. 801,508 and in Sweden December 7, 1888.

In the specification forming part of the -U. S. Letters Patent No. 1,657,056, means are described for causing an intermittently acting electric regulator to be influenced by only the fluctuations of voltage of the machine the excitation of which is immediately controlled by the regulator, said means con sistin of a transformer, the primary winding 0 which is connected to the terminals of the aforesaid machine, while its secondary winding is connected to a coil on the movable member of the regulator. In constructing a transformer for this purpose it has been found, that in order to obtain a suitable manner of operation of the regulator, steps must be taken which very much deviate from the main generator. The winding 12 is fed from an exciter having an armature'winding 61 and magnet winding'62. A resistance 63 in series with the latter is intermittently shortcircuited b a contact 44 of the regulator, which conslsts ofv a swinging member 41 carrying two coils 35 and 52. The coil 35 is influenced by an electromagnet 31 which is voltage of the main generator, and such a current traverses also the coil itself. The coil 52 is influenced by a permanent magnet 51 and is traversed by a current from the secondary winding of a transformer 53, the primary winding of which is connected to the terminals of the armature 61, as has been already described in the specification No. 1,657,056. The attraction between the electromagnet 31 and the coil 35 'is counteracted by a spring 43.

In theaforesaid patent specification the manner of operation-has been described particularly for a constant voltage of the main generator. Fig. 2 of the accompanying drawing, on the contrary, shows certain curves characteristic of the operation occurring when the voltage of the main machine shall be raised again to normal value after having dropped for some reason. On such occasions, the spring force entirel overrules the attraction acting on the co 35, so that the contact will remain in a closed osition; The voltage of the exciter then begins to rise and may be assumed to follow a straight line in the diagram. This is always approximately the case initially, and may with some modification of the connection illustrated be true for a rather long period. The said straight line is in the diagram designated by e.

The voltage E of the main generator can not, by reason of the inertia of the magnetic field, follow immediately the volta e of the exciter, but approaches asymptotica a line which runs parallel to the line e at a 'stance equal to the time constant of the field of the main generator. (In both cases the magnetic saturation is neglected for the purpose of simplicity.) In the same time, the sur lus of the spring force over the attractive orce on the coil 35 decreases, substantially following the line p.

The current in the coil- 52, to which the attractive force acting on that coil is proportional, so that both can be expressed in the diagram by the same curve i, meanwhile increases. As the force acting on the coil 52 on this occasion acts in the same direction as that acting on the coil 31, a'point is sooner or later reached where the force acting on the coil 52 equals the aforesaid surplus p of the spring force, the result being that the pendulum again swings over to the position corresponding to opened contacts. The voltage of the exciter then begins to fall ofi, followin a straight line of the same slope as the ascen ing branch, and the curve representing the voltage of the main machine again is bent ofi towards a constant value. For an ideal regulation, the voltage of the main machine should reach its normal value at the same instant as the voltage of the exciter reaches the value corresponding, under now prevailing conditions, to normal voltage of the main machine. On the other hand it is necessary, that the current in the coil 52 has a possibility of reaching a considerable higher value than that corresponding in the diagram to the point of intersection between the curves p and i, in order that the regulator shall be able to adapt itself to different operating conditions. p

A simple theoretical investigation shows that the curve 2', for a rectilinear formiof the curve e, becomes a common negative logarithmic curve, that is, a curve which, asymptotica'lly approaches a maximum value by a certain time-constant. In fact, the exression for the current i in the coil 52 will the following:

EZL L 1 e 1' r 1, R

where 11. and n, are the numbers of primary and secondary winding turns, respectively, of the transformer 53, 1' and r, the resistances of the prima and seconda circuits, respectively, R the reluctance o the magnetic clrcuit, a the rate of rise of the primary voltage, and e the base of the natural logarithms. The inverse value of the coeflicient of 25 (time) in the exponent of c is the time constant of the curve 1'. From the diagram and the aforesaid condition of maximum value of the current a it is found, that the said time constant must have a value that is at least comparable with the time constant 'of the field of the main generator. As the transformer 53 is an instrument transformer serving only to feed the small coil 52 of a sensitive instrument, it is clear already from the above, that such a transformer havin a time constant comparable with that of t e field ofa large generator essentially differs from the usual design.

The just-mentioned circumstance is further emphasized upon a closer analysis of the factors affecting the time constant. The secondary voltamperes or watts to be iven ofi by the transformer may then first eregarded as given by the properties of the regulator.

The force to be exerted by the coil 52 defines in the first line the ampereturns required therein, and as the-copper quantity is limited by the permissible weight, the minimum watts developed are also defined. The secondary windin 532 of the transformer cannot, however, s calculated for these watts according to the usual principles, considering only the temperature rise, because this would result in a too large internal voltage drop, leavin onl a small fraction of the voltage for t e coi 52. The secondary winding ofv the transformer must be so dimensioned, that the internal voltage drop does not exceed 50%, and already thisrule gives about 100 times-more copper than would be necessary for temperature reasons.

. The primary winding 531 of the transformer, on the other hand, is rincipalzlg de-' termined by the condition, t at the C. ampereturns therein shall not cause too high saturation in the transformer core. This defines the section of the winding, and the length thereof may then be chosen with respect only to the temperature rise. A greater length would reduce the amount of current taken off from the generator 61, but as this need about ten times as much copper as the primary winding. I

In the expression for the time constant of the transformer the reluctance R has not been previously dealt with. The immediate conclusion from the equation appears to be that every factor increasing the reluctance also reduces the time constant. It is therefore highly surprising that the introduction of an air gap 534 in the transformer. core 533 can increase the time constant. A closer examination however shows that this is possible, and the explanation is that the reluctance under the prevailing circumstances is rather far from constant, as had been assumed in the derivation for the sake of simplicity. Since the primary winding carries a rather considerable direct current component, the iron core will continuously operate rather high upon the saturation curve. The magnetic properties of iron are such that the mean tangent of this portion of the curve intersects the B axis at a distance above the OI'lglIl, corresponding to the remanence. It is the inclination of this tangent, that is, the mean value of Lil,

instead of the mean value of H f p but simultaneously it reduces the remanence in a much higher degree, and for a moderate width of the air gap, corresponding to about .001 of the total length of the flux path through iron, this results in an increase of dB 5 d H that is, a decrease of the reluctance. This decrease not only increases the time constant, but also the power given off by a transformer 0 of certain dimensions, or makes it possible to reduce the dimensions for a certain power.

I claim as my invention 1. In electric voltage regulators comprising oscillating contacts, a D. C. generator having an exciting winding connected to said contacts, a coil actuating said contacts, and a transformer having its primary winding connected to said generator and its secondary winding connected to said coil, said secondary winding containing several times as much conducting material as said primary winding.

2. In electric voltage regulators comprising oscillating contacts, a D. G. generaator having an exciting winding connected to said contacts, a coil actuating said contacts, and a transformer having a primary winding connected to said generator, a secondary winding connected to said coil, and an iron core containing an air gap.

In testimony whereof I have signed my name to this specification.

ABLE YTTERBERG. 

